docs: Fix a few typos

[timgates42]

There are small typos in:

• docs/source/index.rst
• guv/event.py
• guv/util/profile.py

Fixes:

• Should read immediately rather than immediatelly.
• Should read previously rather than preveiously.
• Should read development rather than developemnt.

Semi-automated pull request generated by https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md